1. Field of the Invention
The present invention relates to a high-frequency dielectric ceramic member used in the high-frequency bands, such as microwave and millimeter wave bands, and a dielectric resonator, a dielectric filter, a dielectric duplexer, and a communication device, each including the high-frequency dielectric ceramic member.
2. Description of the Related Art
Dielectric ceramic members are widely used for dielectric resonators, circuit boards, etc., in the high-frequency bands, such as microwave and millimeter wave bands.
For example, with respect to dielectric ceramic members used for mobile communication terminals, in order to miniaturize the mobile communication terminals, dielectric ceramic members having a high relative dielectric constant εr and high adhesion strength to plating films are mainly used. Specific examples of dielectric ceramic members mainly used in this application include BaO—Nd2O3—TiO2—PbO-based and BaO—Nd2O3—TiO2—Bi2O3-based dielectric ceramic members with a relative dielectric constant εr of 90, and BaO—Nd2O3—TiO2—PbO—Bi2O3-based dielectric ceramic members with a relative dielectric constant εr of 110.
However, with recent developments in mobile communication, the frequency bands used have shifted to higher frequency bands with shorter wavelengths, giving rise to a new problem. That is, the axis length of a resonator has become excessively short, resulting in a decrease in the non-loading Q factor.
Consequently, there is a demand for a dielectric ceramic member having a relatively low relative dielectric constant εr, a high Q factor, a temperature coefficient τf of resonant frequency that is close to 0 ppm/° C. as much as possible, and high adhesion strength to plating films. By using a material in which the relative dielectric constant εr can be adjusted while controlling the temperature coefficient τf of resonant frequency in the vicinity of 0 ppm/° C., it is possible to provide much more freedom in the design of elements. Therefore, development of such a dielectric ceramic member is also desired.
Hitherto, the following dielectric ceramic members are disclosed.
Japanese Unexamined Patent Application Publication No. 3-216911 discloses a dielectric ceramic member which is composed of a (BaO, MgO)—Re2O3—TiO2-based material, wherein Re is a lanthanide rare-earth element, 50 mole percent or less of BaO being replaced with MgO (first conventional technique). By replacing BaO with MgO in this way, the temperature coefficient τf characteristics can be improved without greatly changing the relative dielectric constant εr or the Q factor.
Japanese Unexamined Patent Application Publication No. 2-252654 discloses a dielectric ceramic member with a composition of BaO—TiO2—Y2O3—Sm2O3—MnO2—MgO (second conventional technique). The dielectric ceramic member has a relative dielectric constant εr of 39 to 44, thus exhibiting satisfactory dielectric characteristics.
Japanese Examined Patent Application Publication No. 61-13326 discloses a dielectric ceramic member composed of a ZrO—SnO2—TiO2-based material (third conventional technique). The dielectric ceramic member has a relative dielectric constant εr of 30 to 40, thus exhibiting satisfactory dielectric characteristics.
However, the first to third conventional techniques described above have the following problems to be solved.
In the first conventional technique, since the MgO content is low and the Re2O3 content is high, a sufficiently high Q factor is not obtained and the temperature coefficient τf is unsuitable for practical use.
In the second conventional technique, although the temperature coefficient τf is in the vicinity of 0 ppm/° C., the MgO content is low (i.e., equal to or less than 1 mole percent), and the relative dielectric constant εr is substantially fixed at approximately 40.
In the third conventional technique, although satisfactory dielectric characteristics are exhibited, the adhesion strength to plating films is low.